The present invention relates to a diagnosis system for a motor vehicle.
Recently, a motor vehicle is equipped with an electronic control system for controlling various components of an engine, such as fuel injectors, thereby improving driveability, exhaust gas emission, fuel consumption and engine power. The electronic control system controls the components based on information represented by output signals from various sensors for detecting engine operating conditions. Accordingly, if malfunctions of components and sensors occur, the engine does not properly operate.
However, because of the complexity of the electronic control system, it is difficult to immediately find out the trouble. Accordingly, a trouble diagnosis device for easily checking the electronic control system should be provided as equipment in an auto shop.
Japanese Patent Application Laid-Open 58-12848 discloses a diagnosis system in which an exclusive checking device is provided for measuring a pulse duration of fuel injection and engine speed, and for checking whether idling speed is normal.
In the disclosed diagnosis system, the number of items displayed on a display is limited to a small number. Accordingly, the operations of the sensors and switches can only be assumed from values indicated on the display of the checking device. For example, the disconnection of a connector for a sensor must be assumed only by checking the output voltage of the sensor which is displayed on the display.
A prior application (U.S. patent Ser. No. 246 996) filed by the applicant of the present patent application discloses a diagnosis system provided with indicators as well as a display. Each of the indicators is arranged to be intermittently turned on in dependency on a signal from a sensor or a switch, thereby enabling a diagnostician to check the operation thereof in an instant.
However, in the system, each indicator corresponds to designated sensors or switches, so that operations of only designated ones can be checked. Accordingly, if operations of all of the sensors and switches are to be checked, a large number of indicators are necessary. Thus, the diagnosis system becomes expensive, large and moreover, difficult to handle. In addition, such a diagnosis system can not be used if the controlling items of the system are increased in the future.